1. Field of the Invention
The present disclosure relates to a method for manufacturing multilayer structure, more particularly to a method for manufacturing the multilayer structure using a feedblock multiplier with thickness-gradient variation.
2. Description of Related Art
The conventional multilayer structure applied to an optical system or any specified purpose is constituted of a plurality of stacked thin films. Any layer inside the structure is designed to be the thin film having various physical properties such as reflective index among the films. Since the multilayer structure is applied to the optical system, the multilayer may be configured to allow the light with a specified wavelength range to pass or block it. This type of optical component with multiple optical films may be assembled by high polymers. In particular, a co-extrusion method is applicable to produce the multilayer for various purposes. Reference is made to FIG. 1.
FIG. 1 shows a schematic diagram of a co-extruding machine Materials are separately input to the machine via a first feeding port 100 and a second feeding port 102. A pre-processing step is firstly performed after mixing the materials. The pre-processing step is such as cleaning, baking including moisture control, and impurity removing. The materials undergoing the pre-processing step are then separated at first time through the first feedblock unit 104, and the material are transported via different channels. In the current example, a second feedblock unit 110 is made to process a second feedblock via the second feedblock unit 110. Therefore, the materials are layer-by-layer mixed, and the transported through the multiple channels.
After that, the fluid after the multiple channels then undergoes a multiplying unit 106 for producing multiple layers. In the meantime, the fluid is directed to a surface material feeding port 108, which forms a protective layer for the structure. Through the multiplying unit 106, the number of the original layers is doubled. The fluid is then compressed through a multilayer extruding unit 111, and output via an extrusion die 112. This extrusion die 112 is configured to uniform the temperature and thickness of the extruded materials, and simultaneously produce the final product with a specified thickness and shape.
After that, a shaping unit 114 is used to fine tune the structure, the product's thickness and direction of transportation of the semi-finished product from the extrusion die 112. A set of rolls 116 flattens the multilayer structure and transports it to a next platform. A stretching roll set 118 is used to perform a uniaxial stretching process onto the multilayer structure by stretching mechanics. A stretching unit 120, which performs a uniaxial or biaxial stretching, may be accompanied with a heating unit 122 for heating the multilayer structure. In consequence the structure is modeled and de-stressed based on its design. The mechanical or thermal/optical properties of the multilayer may be improved. A collecting unit 124 is lastly collected to be the product.
One of the examples of the feedblock in a co-extruder is referred to the conventional way shown in FIG. 2. The shown feedblock 2 includes multiple feeding ports 20, 21, 23, 24 which are receiving different materials. For example, the fluid high polymers are input to a feedblock unit 27 via the feeding ports 20, 21, 23, 24. The mechanics of the feedblock unit 27 is to split the materials into multiple layers, and output from an outlet 22 through extrusion.
The number of the multilayer made by the conventional feedblock is equal to the number by multiplying the inlet number and the number of channels of the feedblock.
FIG. 3A and FIG. 3B schematically show an operational example and the device of a conventional multiplier.
In FIG. 3A, the example describes the operation of multiplier. Numeral 301 indicates the initial input. The input material is split into several transmitting portions, such as four splitting materials 303a, 303b, 303c, and 303d in this example. As required, the relative relations among the input materials 303a, 303b, 303c, 303d may be rearranged as shown. The original inputs 303a, 303b, 303c, 303d are changed to up-to-bottom order such as shown 303c, 303a, 303d and 303b. 
The ordered structure as required may be extended to the longer structure as shown in the figure that is the multiplied multilayer (305). The multilayer structure 307 is formed after extrusion.
FIG. 3B shows a conventional multiplier in one of the examples of the mentioned multiplier.
The shown multiplier may be installed after the feedblock. The input material zone 31 shows the input material is split and entering the device via the feedblock inlets 311, 312, 313, and 314. The material in the inlets is transported through different channels. As the material reaching the shown conversion zones 311′, 312′, 313′ and 314′, the relative positions of channels may be converted as required. When the material reaches the multiplying outlet 32, the number of layers can be multiplied by four other than the change for the relative positions. The final product is then output after extrusion.
In the conventional technology, the polymers may be much stable and uniform as flowing inside the super-multilayer feedblock, such as a disc-shaped super-multilayer feedblock, without thickness, width, or length gradient variation. The stable flowing material may not easily result in too much different velocity, and in theory the flowing stability of the each channel may be great. Therefore the thickness of final output multilayer can be much uniform, and the conventional color spots and blocks can be effectively reduced.
However, in fact, the super-multilayer feedblock with thickness, width or length gradient variation is configured to make the channels with thickness, width or length differences during manufacturing procedure. Since the thickness, width or length of the conventional super-multilayer channels exist variation, the stresses for the internal flow of the channels may be variant. The too much stress variation inside the channels may result in unstable multiple channels as extruding the films. The multilayer may have non-uniform thickness, color spots, or color stripes because of the thickness-gradient variation of the feedblock.